The present invention relates generally to flow cytometers. More particularly, the present invention relates to fluid driving systems for portable flow cytometers or other portable devices.
Flow cytometry is used in a wide variety of applications including hematology, immunology, genetics, food science, pharmacology, microbiology, parasitology and oncology, to name a few. Generally, flow cytometers use light scattering and fluorescence signatures of individual cells to count and measure the properties of the cells as they flow one by one in a thin core stream past a stationary optical detection system.
In most flow cytometry systems, a fluid driving system drives a sample fluid and a number of supporting fluids or reagents into a fluidic circuit. The fluidic circuit arranges the particles in single file, typically using hydrodynamic focussing. In such systems, flow control of the various fluids is extremely important. During hydrodynamic focusing, for example, the relative velocity of each of the fluids can effect the characteristics of the thin core stream. Thus, to achieve optimum core stream characteristics, the velocity of each of the various fluids must be carefully controlled. Likewise, to obtain accurate information on the size and optical characteristics of each cell, the velocity of the cells must be carefully controlled as they pass in front of the optical detection system.
Conventional flow cytometers achieve accurate flow control by using so-called volume-controlled flow. Volume-controlled flow is an open loop system that generates precision pressures by driving precision pumps such as syringe pumps with precision stepper motors. Such systems can provide accurate pressures and flow velocities, but are often bulky, expensive and power hungry. Accordingly, many commercially available cytometer systems are relatively large, bench top type instruments that must remain in a central laboratory environment. This often prevents the use of flow cytometry in remote locations such as at home or in the field.
The present invention overcomes many of the disadvantages of the prior art by providing a fluid driving system that is smaller, less expensive and less power hungry than conventional systems. This is preferably achieved by using a closed-loop system that accepts a less precise and less stable pressure source, which is then adjusted in a closed-loop manner to maintain a constant, desired flow velocity. Such a fluid driving system may be used in portable or wearable cytometers for use in remote locations, such as at home or in the field.
In one illustrative fluid driving system of the present invention, a non-precision pressure source provides an input pressure to a fluid flow path. A downstream flow sensor measures the resulting fluid velocity of the fluid flow path. One or more regulating valves are provided to regulate the pressure that is applied to the fluid flow path. A controller, which receives a signal from the flow sensor, controls the one or more valves so that the fluid velocity of the fluid flow path is at a desired level.
For some applications, the non-precision pressure source may be manually powered. A manually powered pressure source may include, for example, a bulb with check valve or a plunger. For other applications, the non-precision pressure source may be a non-precision electrically powered pump such as an electrostatically actuated meso-pump. In either case, the non-precision pressure is preferably provided to a first pressure chamber. A first valve is then provided for controllably releasing the pressure in the first pressure chamber to a second pressure chamber. A second valve is provided in the second pressure chamber for controllably venting the pressure in the second pressure chamber.
The controller controllably opens the first valve and closes the second valve when the fluid flow in the downstream fluid stream drops below a first predetermined value and controllably opens the second valve and closes the first valve when the fluid flow in the downstream fluid stream increases above a second predetermined value. Each valve is preferably an array of electrostatically actuated microvalves that are individually addressable and controllable.
It is contemplated that any residual variation in flow rate and in sample volume may be compensated for through electronic signal processing, based on accurate flow rate information collected by time-of-flight particle velocity measurements performed by a downstream optical detection system.